1. Field of the Invention
The invention relates generally to paper handling for a typewriter and, more particularly, to apparatus for advancing a sheet of paper to a desired first line printing position.
2. Statement Regarding the Prior Art
Various apparatus has been proposed and implemented for semi-automatically inserting paper into a typewriter. Generally, however, such apparatus has had limited appeal because complicated special purpose mechanisms were required that unduly increased machine costs and because the operator was required to learn a somewhat involved procedure to achieve a result that could be accomplished manually with only a moderate effort.
The increase in costs and complexity arises because provision must be made for operator indication of the desired first line printing position and because the paper path must be prepared for paper insertion, for example, by moving a paper hold-down device at the printing line out of the paper path so as not to interfere with the leading edge of the incoming page (or pack including carbons).
Various selector devices have been used to allow the operator to indicate a desired first line printing position. Typically a dial (see e.g., U.S. Pat. Nos. 3,960,258 and 3,276,562) or a selection lever (see e.g., U.S. Pat. No. 2,463,259) is employed for indicating the desired first printing line and these devices are coupled to mechanical stops or clutch disengaging devices to limit total paper advance.
The problem of getting the leading edge of the paper past the printing zone has proven to be troublesome one. To achieve the basic typing function, i.e., the crisp printing of characters, the paper must be held snugly to the platen in the printing zone. But the paper hold-down device, typically a series of rollers on a bail, does not, when in operative position, allow easy passage of the paper past the printing zone. In fact, jamming typically occurs if the device is not manually withdrawn, and such jamming may cause unacceptable creasing of the paper.
One solution of this problem is to use a shaped guide plate (see e.g., U.S. Pat. No. 2,353,407) rather than rollers to hold the paper in position, but such arrangement would appear to have problems holding the paper effectively at the print line, especially if clearance provision must be made to thick carbon packs. A more common solution has been to provide an automatic drive arrangement for the paper hold-down bail (see e.g., U.S. Pat. Nos. 2,204,243; 2,210,168; 3,292,762; 3,960,258; and 4,031,195).
There is, of course a significant cost penalty for such limited purpose automatic drive mechanisms and there is possibly a maintenance problem if, for example, rearward hand or arm pressure is accidentally applied against the bail when it is being driven forward.
Hence, with prior art devices the convenience of semi-automatic paper insertion has involved significant cost penalties and special set up procedures that are rather distinct from manual paper insertion and, therefore, are not convenient for the operator to learn.